Network Node, User Equipment and Methods Therein for Adjusting the Transmit Timing of Uplink Transmissions

1. A method in a user equipment for adjusting a transmit timing of uplink transmissions to a network node in a telecommunications system, the method comprising: determining a change to a second timing reference serving cell in a group of serving cells sharing an advance timing value, the second timing reference serving cell being different from a first timing reference serving cell currently being used as the timing reference serving cell for the group of serving cells; and applying an incremental adjustment of transmit timing for uplink transmissions for the serving cells in the group of serving cells, wherein the incremental adjustment comprises two or more adjustments gradually applied in the incremental adjustment; wherein the determining comprises receiving a triggering event based on at least one triggering rule; wherein the at least one triggering rule is based on a timing threshold; and wherein the triggering event is provided when an adjustment in uplink transmission timing in response to the second timing reference serving cell would cause a change that is greater to or equal to the timing threshold.

2. The method of claim 1 , further comprising receiving an adjustment request or an adjustment notification from the network node.

3. The method of claim 1 , wherein, in response to a magnitude of a difference between reception timings of downlink reception transmissions of the first timing reference serving cell and the second timing reference serving cell being above a threshold, a magnitude of the incremental adjustment is less than the magnitude of a difference between the reception timings of downlink reception transmissions of the first timing reference serving cell and the second timing reference serving cell.

4. The method of claim 1 , wherein the applying comprises applying an incremental advance or retreat of the uplink transmission timing.

5. The method of claim 1 , wherein the applying comprises: analyzing a total adjustment to be made with respect to a timing threshold; determining a number of increments of the incremental adjustment based on the analyzing.

6. The method of claim 1 , wherein the applying comprises: choosing an activated secondary serving cell with a lowest index value as a new timing reference serving cell; applying the incremental adjustment with respect to the activated secondary serving cell with the lowest index value.

7. The method of claim 1 , wherein the applying is based on at least one application rule.

8. The method of claim 7 , wherein the at least one application rule provides an adjustment amount for each incremental step of the adjustment.

9. The method of claim 7 , wherein the at least one application rule is associated with one or more of the following: a bandwidth of transmitted signals; a type of carrier aggregation scheme; a user equipment activity factor; a type of physical channel; whether serving cells are co-located or not; radio characteristics.

10. The method of claim 7 , wherein the application rules are provided by the network node.

11. The method of claim 1 , further comprising receiving at least one parameter associated with the incremental adjustment and utilizing the at least one parameter in the applying of the incremental adjustment.

12. The method of claim 11 , wherein the at least one parameter is at least one of: a maximum amount of magnitude in an uplink transmission timing change per increment; a minimum aggregate uplink transmission timing adjustment rate; a maximum aggregate uplink transmission timing adjustment rate.

13. The method of claim 1 , wherein determining a change to a second timing reference serving cell comprises changing the timing reference serving cell for the group of serving cells from the first timing reference serving cell to the second timing reference serving cell.

14. A user equipment adapted to adjust a transmit timing of uplink transmissions to a network node in a telecommunications system, the user equipment comprising: processing circuitry configured to: determine a change to a second timing reference serving cell in a group of serving cells sharing an advance timing value, the second timing reference serving cell being different from a first timing reference serving cell currently being used as the timing reference serving cell for the group of serving cells; apply an incremental adjustment of the transmit timing for uplink transmissions for the serving cells in the group of serving cells, wherein the incremental adjustment comprises two or more adjustments gradually applied in the incremental adjustment; and receive a triggering event based on at least one triggering rule; wherein the at least one triggering rule is based on a timing threshold; and wherein the triggering event is provided when an adjustment in uplink transmission timing in response to the second timing reference serving cell would cause a change that is greater to or equal to the timing threshold.

15. The user equipment of claim 14 , wherein the processing circuitry is further configured to receive an adjustment request or an adjustment notification from the network node.

16. The user equipment of claim 14 , wherein the processing circuitry is further configured to apply an incremental advance or retreat of the uplink transmission timing.

17. The user equipment of claim 14 , wherein the processing circuitry is further configured to: analyze a total adjustment to be made with respect to a timing threshold; determine a number of increments of the incremental adjustment based on the analysis.

18. The user equipment of claim 14 , wherein the processing circuitry is further configured to choose an activated secondary serving cell with a lowest index value as a new timing reference serving cell; apply the incremental adjustment with respect to the activated secondary serving cell with the lowest index value.

19. The user equipment of claim 14 , wherein the processing circuitry is further configured to apply the incremental adjustment based on at least one application rule.

20. The user equipment of claim 19 , wherein the at least one application rule provides an adjustment amount for each incremental step of the adjustment.

21. The user equipment of claim 19 , wherein the at least one application rule is associated with one or more of the following: a bandwidth of transmitted signals; a type of carrier aggregation scheme; a user equipment activity factor; a type of physical channel; whether serving cells are co-located or not; radio characteristics.

22. The user equipment of claim 19 , wherein the application rules are provided by the network node.

23. The user equipment of claim 14 : further comprising radio circuitry configured to receive at least one parameter associated with the incremental adjustment; wherein the processing circuitry is configured to utilize the at least one parameter in the application of the incremental adjustment.

24. The user equipment of claim 23 , wherein the at least one parameter is at least one of: a maximum amount of magnitude in an uplink transmission timing change per increment; a minimum aggregate uplink transmission timing adjustment rate; a maximum aggregate uplink transmission timing adjustment rate.

25. The user equipment of claim 14 , wherein the processing circuitry is further configured to determine a change to a second timing reference serving cell by changing the timing reference serving cell for the group of serving cells from the first timing reference serving cell to the second timing reference serving cell.